Technical note Effect of corrosion inhibitors on scale removal during pickling of mild steel

Abstract

The effect of certain heterocyclic organic inhibitors (indole, indole acetic acid, indole butyric acid, and 3-acetyl indole) on scale dissolution during the pickling of mild steel in 10%HCl has been investigated by means of corrosion potential measurements and scanning electron microscopy (SEM). The results have shown that indole and 3-acetyl indole have the highest inhibition efficiencies of 98 and 96% respectively. However, while 3-acetyl indole slightly retarded dissolution of the oxide scale, indole accelerated the scale removal process.     

FeCo基大块非晶合金盐雾与电化学腐蚀研究

通过电化学测试方法与中性盐雾腐蚀实验研究Fe24 xCo24-xCr15Mo14C15B6Y2 (X=0, 2, 4, 6, 17)块体非晶合金的耐蚀性。合金在1 mol/L HCl中出现了宽的钝化区,其EIS图谱均由单一容抗弧组成,显示出良好耐蚀性;结合极化曲线与交流阻抗结果分析可得合金耐蚀性随着Co含量的增加先增大后减小,当Co含量为20%时合金耐蚀性最好。利用能谱分析(EDS)与原子力显微镜(AFM)对合金的中性盐雾腐蚀结果进行分析,可知它们的腐蚀产物主要由铁和钴的氧化物以及它们的氯化物组成。同时FeCo基大块非晶合金腐蚀程度随着Co含量的变化而变化,其盐雾腐蚀耐蚀性规律与电化学腐蚀耐蚀性规律一致。     

表层纳米化对钛合金电化学腐蚀影响的研究进展

表层纳米化处理可以改变材料表层的组织结构,提高材料的表面性能,而钛合金综合性能优异,有着广泛的应用,可以通过表层纳米化技术在钛合金表层制备出一定厚度的纳米层,进一步提升钛合金的耐腐蚀性能.本文介绍了表层纳米化技术和钛合金表层纳米化的作用机理,并综述了目前国内外表层纳米化对钛合金电化学腐蚀影响的研究进展,重点阐述了表层纳...     

Hg和Ga元素对Mg阳极材料组织和电化学腐蚀性能的影响(英文)

采用动电位极化、恒电流和交流阻抗测试方法研究了Hg和Ga元素对Mg2%Hg,Mg2%Ga和Mg2%Hg2%Ga合金电化学腐蚀性能的影响,并用扫描电镜、X射线衍射和能谱分析了上述合金的显微组织和腐蚀表面形貌。结果表明:Mg2%Ga合金是固溶体,Mg-2%Hg和Mg-2%Hg2%Ga合金的晶界有白色第二相。Mg-2%Ga合金的平均电位为1.48V,腐蚀电流密度为0.15mA/cm2,电化学活性差,耐腐蚀性能好。Mg-2%Hg-2%Ga合金的平均电位1.848V,腐蚀电流密度为2.136mA/cm2,电化学活性好,耐腐蚀性能差。MgHgGa合金的活化机制是Hg和Ga原子的溶解沉积。     

Anion effects on the stress corrosion cracking behaviour of aluminium alloys

The stress corrosion cracking behaviour of plate material of the aluminium alloys 2024‐T351, 8090‐T8171, 7475‐T651, and 7075‐T7351 was investigated performing constant load tests. Short transverse tensile specimens were permanently immersed in aerated aqueous 0.6 M Na₂Cl solutions with additions of Na₂SO₄, NaNO₃, NaHCO₃, NH₄HCO₃, Na₂HPO₄, Na₂SO₃ or Na₂CO₃. The concentration of the added salts was 0.06 M. The applied stress was 100 MPa, except with 7075‐T7351 specimens, which were loaded at 300 MPa. Environment induced failure was not observed in neutral 0.6 M NaCl solution. The various salts added promoted intergranular stress corrosion cracking with the alloys 2024‐T351, 8090‐T8171, and 7475‐T651. Threshold stresses were generally below 100 MPa. For 8090‐T8171 exposed to chloride containing electrolytes with additions of sulfate, hydrogen phosphate, or sulfite, threshold stresses were approximately 100 MPa or higher. Similar results were obtained for 7475‐T651 plate when immersed in chloride‐hydrogen phosphate and chloride‐carbonate solutions. Alloy 7075‐T7351 was resistant against intergranular stress corrosion cracking. Specimens suffered pitting corrosion during immersion in the corrosive environments. Failure observed with 7075‐T7351, in particular when exposed to the chloride‐nitrate solution, was associated with reduction of cross‐sectional area due to pitting and transgranular stress corrosion cracking.     

Composition and processing effects on the electrochemical characteristics of biomedical titanium alloys

The electrochemical behaviour of the Ti–13Nb–13Zr and Ti–6Al–4V ELI alloys with martensitic microstructures was investigated by polarization and electrochemical impedance spectroscopy (EIS) in Ringer’s solution. The impedance spectra were interpreted by a two time-constants equivalent circuit. Both investigated alloys showed high corrosion resistance, but the thin and uniform passive film on the Ti–6Al–4V ELI alloy surface was more protective. The inner barrier and outer porous layer were highly resistant and capacitive. However, thicker and more porous passive film on the Ti–13Nb–13Zr alloy surface may be beneficial for osteointegration. The suitable thermomechanical processing improved the corrosion resistance of Ti–13Nb–13Zr alloy.     

Compositional effects of Zr-rich multi-component brazing alloys on the corrosion of Zr alloy joints

High-temperature corrosion of Zircaloy-4 joints brazed by various Zr(Ti)–Cu–Ni-based multi-component alloys was studied to draw up the compositional guideline of the brazing alloy. From the compositional and microstructural effects of the joints on the corrosion, there was strong evidence for galvanic corrosion susceptibility of primary α-Zr grains (usually Sn-containing) owing to alloying of nobler Ti and its concentration gradient in a joint, inducing a microgalvanic corrosion. The Ti concentration for corrosion inhibition was proposed to be less than about 1.0 at.%. The results clearly demonstrate that the exclusion of Ti is needed for the use of Zr-rich multi-component brazing alloys.     

Formation of corrosion resistant plasma electrolytic oxidation coatings on aluminium alloy with addition of sodium tungstate species

Plasma electrolytic oxidation (PEO) coatings were formed in silicate based electrolytes without and with the addition of sodium tungstate on AA?6063 aluminium alloy. Microstructure, composition and corrosion resistance of PEO coatings were investigated by scanning electron microscopy, X-ray diffraction and electrochemical impedance spectroscopy and potentiodynamic polarisation test respectively. The effects of additive sodium tungstate were examined. The results showed that the additive containing PEO coatings were of dense structure with additional phase (WO₃) and of less cracks than the additive free PEO coating. In addition, additive containing coatings were of better corrosion resistance than the additive free PEO coating, which was confirmed by electrochemical impedance spectroscopy and potentiodynamic polarisation tests. Furthermore, long time immersion test revealed that the PEO coated alloy with the addition of 12?g?L^??1 sodium tungstate maintained high impedance over 82?h in 3.5?wt-%NaCl, while the PEO coating without additive was unable to protect the substrate after such long time immersion.     

Understanding the effects of electrode inhomogeneity and electrochemical heterogeneity on pitting corrosion initiation on bare electrode surfaces

The effects of electrode inhomogeneity (EI) and electrochemical heterogeneity (EH) on pitting corrosion initiation have been analysed by revisiting research findings reported in the literature and experimental evidences obtained in our laboratories using the wire beam electrode (WBE) method. Two mechanisms of pitting corrosion initiation have been identified on bare metal surfaces exposed directly to electrolytes. For WBE surface under free corrosion or low anodic polarisation conditions the initiation of pitting corrosion was found to be due to the disappearance of minor anodes, leading to accelerated dissolution of a few remaining major anodes. The nucleation stage of pitting corrosion appeared to be controlled by EI, while the propagation stage appeared to be determined by EH. For WBE surface under large anodic polarisation the initiation of pitting corrosion was found to be due to the formation of active new anodic sites, which is in agreement with the conventional mechanism of pitting nucleation.     

The effects of spark anodizing treatment of pure titanium metals and titanium alloys on corrosion characteristics

This study evaluated the surface characteristics of oxide films on commercially pure titanium metals (CP-Ti; Grade 2 and Grade 3) and titanium alloy (Ti6Al4V and Ti6Al7Nb) samples formed by an anodic oxidation treatment, and investigated the effects of anodization on the corrosion characteristics. FE-SEM, XRD, and Raman spectroscopy were used to evaluate the micromorphology and crystalline structure of the oxide films. The corrosion resistance of the sample groups was evaluated using open-circuit potential and cyclic polarization tests. After anodic oxidation up to dielectric breakdown with the same electric current, 150-200 nm-sized pores were distributed homogeneously on pure titanium metal samples, partially occluded pores were observed on the Ti6Al4V alloy, and there was an inhomogeneous size and distribution of pores on the Ti6Al7Nb alloy. The titanium dioxide films formed through anodic oxidation contained a phase mixture of anatase and rutile. The cyclic polarization tests showed that all the tested sample groups were not susceptible to localized corrosion. The as-received and anodically oxidized CP-Ti grade 3 groups showed a higher corrosion resistance than the other groups. The mean E_corr values of the anodically oxidized sample groups, except for the anodized Ti6Al7Nb alloy, showed higher values than those of the respective as-received sample groups. In particular, the Ti6AL7Nb alloy showed a statistically higher E_corr value in the anodized group than in the as-received group (p < 0.05).     

Novel corrosion experiments using the wire beam electrode: (II) Monitoring the effects of ions transportation on electrochemical corrosion processes

An electrochemically integrated multi-electrode system namely the wire beam electrode (WBE) has been applied for the first time to study the effects of the transportation of electrochemically active species on the process, rate and pattern of electrochemical corrosion. The objective of this work is to demonstrate the applicability of the WBE method for investigating ion transportation related corrosion processes. A series of experiments have been carried out using WBEs made from mild steel and stainless steel wires. The WBE working surfaces were exposed to simulated diffusion-controlled corrosion environments where there were diffusion induced ions concentration gradients (termed diffusion-corrosion environment). Corrosion potential and current distribution maps (CPCD maps) were measured from WBE surfaces in continuous bases. Typical patterns have been identified from CPCD maps and the characteristics of these patterns have been found to depend heavily upon the type of electrode material and the type of corrosive ion. For mild steel WBE surface exposed to a diffusion-corrosion environment containing NiSO₄ or FeCl₃, the characteristic pattern in CPCD maps was found to emulate NiSO₄ or FeCl₃ concentration gradients, suggesting an ion-concentration controlled corrosion behaviour. However, when the mild steel WBE surface was exposed to a diffusion-corrosion environment containing NaCl, the characteristic pattern was found to show higher cathodic currents along the WBE edges with the magnitude decreasing in a contour-like manner towards the centre of the WBE surface, suggesting an oxygen concentration-controlled corrosion behaviour. When a stainless steel (SS316L) WBE surface was exposed to a diffusion-corrosion environment containing NiSO₄ or NaCl, the corrosion pattern appeared to be mainly determined by the random distribution of weak sites in passive film. When the SS316L WBE was exposed to a diffusion-corrosion environment containing FeCl₃, the CPCD map revealed a characteristic pattern that shows localised damage to passive film. This work demonstrates that the recognition and analysis of characteristic maps from WBE measurements can be used as a means of studying diffusion, migration and other forms of mass transportation related electrochemical corrosion processes.     

Thickness effects on corrosion and wear resistance properties of micro-arc discharge oxide coatings on AZ91D magnesium alloys

The microarc oxidation coatings with difference thickness were synthesized on AZ91D magnesium alloy. The microstructure and phase structure of the coatings were analyzed using SEM and XRD, the tribological properties and corrosion resistance behaviour of the coatings were also investigated. The results show that the coating contains two layers, a porous outer layer and relatively dense inner layer. The microhardness of the MAO coatings is four to six times higher than that of the magnesium alloy substrate. The MAO coatings have much better wear-resistance and corrosion resistance abilities than those of magnesium alloy substrate, but possess higher friction coefficient. The results further indicate that there is an optimization thickness for corrosion and wear resistance.     

The effects of lanthanum on microstructure and electrochemical properties of Al–Zn–In based sacrificial anode alloys

In order to improve the non-uniform corrosion of Al–0.5Zn–0.03In–1Mg–0.05Ti alloys, Al–5Zn–0.03In–1Mg–0.05Ti–xLa (x = 0.3, 0.5 and 0.7 wt.%) alloys were developed. Microstructures and electrochemical properties of the alloys were investigated. The results show that the optimal microstructures and electrochemical properties are obtained in Al–5Zn–0.03In–1Mg–0.05Ti–0.5La alloy. The main precipitate phase is Al₂LaZn₂ particles. The excellent electrochemical properties of Al–5Zn–0.03In–1Mg–0.05Ti–0.5La alloy is mainly attributed to fine grains and grain boundaries containing fine Al₂LaZn₂ precipitates. At the same time the fine grains can improve the non-uniform corrosion of Al–0.5Zn–0.03In–1Mg–0.05Ti alloy.     

The effect of chemical species on the electrochemical reactions and corrosion product layer of carbon steel in CO2 aqueous environment: A review

This study summarizes the chemical effects that can occur during the corrosion process of carbon steel in a CO₂-saturated aqueous environment. Particularly, it focuses more on the results that small chemical contaminations in the environment have on the corrosion process. Underground waters present complex chemistry with several different dissolved ions (chlorides, carbonates) even in high concentrations that impact substantially the corrosion rates of these materials. Moreover, gas impurities present in the gas mixture, such as oxygen in carbon capture and storage applications, constitute a supplementary form of significant contamination in the CO₂-saturated aqueous environment. In particular, the effect on both electrochemical reactions and corrosion product layer is examined for several chemical species that are commonly present either in the gas mixture or in underground waters.     

The effects of sulfate reducing bacteria on corrosion of carbon steel Q235 under simulated disbonded coating by using electrochemical impedance spectroscopy

The effect of sulfate reducing bacteria (SRB) on the corrosion of the carbon steel Q235 has been investigated in the crevice under the simulated disbonded coating in the soil-extract solutions (SES). The results of electrochemical impedance spectroscopy (EIS) show that the corrosion rate is inhibited in the SES with SRB during the stationary phase of SRB, but enhanced during the death phase. The comparison of the polarization (R_p) and the charge transfer resistances (R_t) has indicated that the biofilm seriously influences the reactive procedure of metal/solution interface. SRB is found in the pits on the surface of the steel.     

Microstructure effects on the electrochemical corrosion properties of Mg – 4.1% Ga – 2.2% Hg alloy as the anode for seawater-activated batteries

Mg–Ga–Hg alloy is a new material with special electrochemical corrosion properties that make it ideal for use in seawater-activated battery anodes. The effects of microstructure and phase transformation on the electrochemical properties of the Mg – 4.1% Ga – 2.2% Hg alloy were studied and compared with Mg–Al system alloys. The results show that the Mg – 4.1% Ga – 2.2% Hg alloy, when used as an anode, has an appropriate corrosion potential in a half-cell test and superior electrochemical properties in a single cell assembled with CuCl. The Mg₃Hg and Mg₂₁Hg₅Ga₃ phases of the alloy influence its corrosion behaviour and provide a steady corrosion potential during the discharge process.     

The effects of polyethylene glycol (PEG) as an electrolyte additive on the corrosion behavior and electrochemical performances of pure aluminum in an alkaline zincate solution

The effects of zinc oxide and/or polyethylene glycol (PEG) as electrolyte additives on the corrosion and electrochemical performances of pure aluminum in 4.0 M KOH solutions were investigated by means of hydrogen collection, polarization curve, galvanostatic discharge, scanning electron microscopy (SEM), and energy dispersive analysis of X‐ray (EDAX). The addition of ZnO markedly inhibited the corrosion of aluminum in 4.0 M KOH solutions, resulting from the deposition of zinc with high hydrogen evolution overpotential in aluminum surfaces. The introduction of PEG in the alkaline zincate solution obviously improved the deposition of zinc by increase in the overpotential of zinc deposition, thus the corrosion rate of aluminum in the alkaline zincate solutions with PEG was further decreased. The enhancement effect of PEG on the inhibition of zinc oxide first increased and then decreased with increasing the content of PEG in the electrolyte. The electrolyte system with 0.2 M ZnO and 2.0 mM PEG presented the highest inhibition efficiency (98.8%) for the corrosion of aluminum. The results of galvanostatic discharge indicated that the aluminum anode shows excellent discharge performances in the 4.0 M KOH solution with 0.2 M ZnO and 2.0 mM PEG.